1. Field of the Invention
The present invention relates to washing machines, and more particularly, to a washing machine control method, in which an amount of laundry in the washing machine is determined based on a computed average of pulse width modulation values at the time of stopping the drive of a motor and the motor's rotational angle as the motor freewheels to a stop.
2. Discussion of the Related Art
Generally speaking, a washing machine is an apparatus for washing laundry by performing washing, rinsing, and dewatering steps in accordance with a wash course as selected by a user Washing machines are typically categorized according to washing type is and may include pulsator, agitator, and drum types.
To perform washing using a washing machine in which laundry has been placed, a wash course is selected to determine a wash pattern, water is supplied to the washing machine according a predetermined water level based on a sensed amount of laundry in the washing machine, and washing is performed based on the predetermined water level. After the water reaches the predetermined level, however, a motor is driven to perform washing. In doing so, the laundry absorbs a portion of the water, and the water level is lowered such that water should be re-supplied until reaching the desired level. Accordingly, it is difficult to accurately sense the amount of laundry in the washing machine.
A general drum-type washing machine, as shown in FIG. 1, is comprised of a tub 2 for holding washing water and a drum 3 for holding laundry, rotatably installed in the tub and receiving a drive force of a motor 4 via a belt 5 and pulleys 41 and 31 to perform washing related steps. With laundry placed inside the drum 3, the tub 2 is filled with water to a predetermined level. Under such a load, the motor 4 is driven under the control of a microcomputer (not shown), to proceed the washing, rinsing, and dewatering steps. Once a washing step is initiated, water is supplied to the tub 2 to a predetermined level, and the motor 4 is driven to rotate the drum 3 forward and reversely so that the laundry is evenly soaked in the water, whereupon the laundry partially absorbs the water so that the water level drops below the predetermined level.
The microcomputer of the above washing machine detects the water level to determine whether a water re-supply operation is needed. That is, if the water level has dropped below the predetermined level, it is determined that a water re-supply operation is needed, in which case the rotation (drive) of the drum 3 is stopped while water is re-supplied to the predetermined level, after which the rotation of the drum 3 begins anew. The microcomputer repeats the above steps until a predetermined time expires, while counting the number of the water re-supply operations, to determine the amount of laundry based on the counted number of the water re-supply operations during the predetermined time. To accomplish this, the microcomputer is provided with a lookup table for storing a set of reference values, which are preset for a given washing machine, to determine the laundry amount as being one of a predetermined set of laundry loads, e.g., a small, medium, or large laundry load. The reference values can be known since a larger laundry load absorbs more water and results in a greater number of water re-supply operations; conversely, fewer water re-supply operations would indicate smaller laundry loads.
After the desired water supply level is reached through a number of water re-supply operations, the washing step is executed based on a laundry amount determined by the above process. In such a method, however, the time for the water supply to reach the desired level is excessive, which unnecessary prolongs the washing step and tends to waste water. Moreover, a determination of the laundry amount using a lookup table is inherently inaccurate.